1. Field of the Invention
The invention relates to a preparation for the abhesive coating of baking tins, cake tins, frying pans, metal pots and the like, which consists predominantly of heat-curable polysiloxane resins and may contain hardeners, pigments, fillers, cross-linking and spreading agents, as well as solvents.
2. Description of the Prior Art
It is well known that baking tins, cake tins, frying pans, metal pots and cooking utensils may be provided with a release coating in order to prevent baked or cooked foods, especially those containing sugar, adhering to or not separating from the surface of the metal.
Release agent coatings of polytetrafluoroethylene which are fused onto the surface of the tin and which mostly consist of aluminum or tin plate are known. These coatings however have several disadvantages. One serious disadvantage is that the fusion temperatures required for applying the polytetrafluoroethylene to the surface of the metal are so high that the metallurgical properties, especially of aluminum molds, are affected. It is a further disadvantage that the hardness of the coating is inadequate. This leads to mechanical damage to the polytetrafluoroethylene layer as the molds, tins, and the like are used and, as a result, the baked material once again commences to adhere. Organopolysiloxane resins have also already been recommended for the abhesive coating of tins which come into contact with sugar and sugar-containing foods.
U.S. Pat. No. 3,925,276 discloses the use of an organopolysiloxane resin with silanol groups, which is obtained in a special manner. Apart from a solution of this resin in xylene, the preparation for the coating additionally contains a viscosity-affecting solvent, iron octoate, as a hardener for the silicone resin, and slight amounts of a liquid methylphenylsiloxane. Since the silicone resin exhibits inadequate release action by itself, it may be assumed that the relatively good abhesive properties may be substantially attributed to the liquid siloxane, which has been added since it is only limitedly miscible with the resin and therefore accumulates at the surface. It is a disadvantage that, on repeated use, these silicone oil portions present in the surface are removed and the release action is diminished in the course of usage.
A release agent is described in German Offenlegungsschrift No. 27 00 038 which is based on the state of the art as defined by U.S. Pat. No. 3,925,276. The essential characteristic of this German Offenlegungsschrift is the fact that, in addition to silicone oil, about 10 to 40 weight percent of a fluorinated hydrocarbon polymer is added in a finely dispersed form to the previously described silicone resin. The particles of fluorinated hydrocarbon polymer are firmly tied into the matrix of the cured silicone resin so that, even after the removal of the silicone oil from the surface, a certain long-term effect is maintained. It is however a disadvantage of the added fluorinated hydrocarbon polymer particles that, especially at higher levels of addition, the mechanical properties of the coating are once again impaired.